USPTO Patents Application 10687850

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(19)

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(43) Date of publication:

06.05.1998 Bulletin 1998/19

EuropSisches Patentamt
European Patent Office
Office europeen des brevets (11) EP 0 840 122 A2

EUROPEAN PATENT APPLICATION

(51) lot Cl. 5 : G01 N 33/487, G01 N 33/49

(21) Application number: 97118039.3

(22) Date of filing: 17.1 0.1 997

(84) Designated Contracting States:

• Johnson, Larry D.

AT BE CH DE DK ES R FRGB GR IE IT LI LU NIC

Elkhart, IN 4651 4 (US)

NL PT SE

• Musho, Matthew K.

(30) Priority: 30.10.1996 US 740564

Granger, Indiana 46530 (US)
• Perry, Joseph E.

(71) Applicant: Bayer Corporation

Osceola, Indiana 46561 (US)

Pittsburgh, PA 15205-9741 (US)

(74) Representative:

(72) Inventors:

• Chariton, Steven C.
Osceola, Indiana 46561 (US)

Kirchner, Dietrich, Dr.
c/o Bayer AG
Konzernbereich RP
Patente und Lizenzen
51368 Leverkusen (DE)

(54) Method and apparatus for calibrating a sensor element

(57) A method and apparatus are provided for cali-
brating a sensor for determination of analyte concentra-
tion. The meter includes a sensor for receiving a user
sample to be measured and a processor for performing
a predefined test sequence for measuring a predefined
parameter value. A memory can be coupled to the proc- 2ba-
essor for storing predefined parameter data values. A
calibration code is associated with the sensor and read *°* ~
by the processor before the user sample to be meas-
ured is received. The calibration code is used in meas-
uring the predefined parameter data value to toa*
compensate for different sensor characteristics.

MEMORY

SI

ON/OFF
INPUT

SYSTEM
FEATURE
INPUT

AUTOCALIBRATION
READING

MICROPROCESSOR
82

ALARM
69

DISPLAY

DATA
PORT
90

SENSOR
32

BATTERY
MONITOR
88

CM

<

CM
CM

FIG.5

Prtrtad by Xorax (UK) Business Services
2.1 $.2/3.4

1

EP 0 840 122 A2

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Description

Field of the Invention

The present invention generally relates to a sensor,
and, more particularly, to a new and improved method
and apparatus for calibrating a sensor element.

Description of the Prior Art

The field of clinical chemistry is concerned with the
detection and guantitation of various substances in
body material, typically body fluids such as blood, urine
or saliva. In one important aspect of this field, the con-
centration of naturally occurring substances, such as
cholesterol or glucose, in an individual's blood is deter-
mined. One of the most frequently used analytical
devices in clinical chemistry for determining the concen-
tration of an analyte in a fluid sample is the test sensor.
Upon contacting the test sensor with the fluid sample,
certain reagents incorporated into the sensor react with
the analyte whose concentration is being sought to pro-
vide a detectable signal. The signal may be a change in
color as in the case of a colorimetric sensor or a change
in current or potential as in the case of an electrochem-
ical system. For a particular class of electrochemical
sensors, i.e. amperometric sensors, the detected cur-
rent is proportional to the concentration of the analyte in
the fluid sample being tested. Those systems which
employ an enzyme in the reagent system may be
refened to as biosensors since they rely on the interac-
tion of the enzyme (a biological material) with the ana-
lyte to provide the detachable response. This response,
whether it be a change in color or in cunent or in poten-
tial, is typically measured by a meter, into which the sen-
sor is inserted, which meter provides a readout of the
analyte concentration such as by means of a LCD sys-
tem.

In particular, the determination of glucose in blood
is of great importance to diabetic individuals who must
frequently check the level of glucose in connection with
regulating the glucose intake in their diets and their
medications. While the remainder of the disclosure
herein will be directed towards the determination of glu-
cose in blood, it is to be understood that the procedure
and apparatus of this invention can be used for the
determination of other analytes in other body fluids or
even non-fluid body materials such as the detection of
occult blood in fecal material upon selection of the
appropriate enzyme. In addition such sensors can be
used in, for example, testing for meat spoilage or foreign
substances in well water.

Diagnostic systems, such as Wood glucose meas-
uring systems, typically calculate the actual glucose
value based on a measured output and the known reac-
tivity of the reagent sensing element used to perform
the test The latter information can be given to the user
in several forms including a number or character that

they enter into the instrument, a sensed element that is
similar to a test sensor but which is capable of being
recognized as a calibration element and its information
read by the instrument or a memory element that is

5 plugged into the instrument's microprocessor board and
is read directly.

Various anangements have been used to provide
lot calibration information into the instrument. The base
method requires the user to enter a code number which

10 the instrument can use to retrieve calibration constants
from a lookup table. U.S. Patent 5,266,179 discloses a
resistor whose resistance value can be measured by
the instrument. From the resistance value the calibra-
tion constants are recovered.

is The Advantage system and Accucheck series of
glucose meters marketed by Boehringer Mannheim
Diagnostics employ a reagent calibration method based
on an integrated circuit (IC) chip. This chip is included in
each reagent package purchased by the customer.

20 Information about how the instrument is to calibrate
itself for that particular lot of reagent is contained on the
IC. The customer must attach the IC to the instrument
by slipping the IC into a connection port located on the
instrument The IC may be interrogated for its informa-

25 tion each time the user turns on the instrument. All
these systems require the user to interact directly for
calibration information to be available to the instrument
and therefore, for a successful glucose number to be
calculated.

30

Summary of the Invention

Important objects of the present invention are to
provide a new and improved method and apparatus for
35 calibrating a sensor and to provide such method and
apparatus that eliminates or minimizes the need for user
interaction.

In brief, a method and apparatus are provided for
calibrating a sensor element. The sensor element is

40 used in a sensor system which includes a sensor meter,
a sensor element for receiving a user sample to be ana-
lyzed and a processor for performing a predefined test
sequence for measuring a predefined parameter value.
A memory is coupled to the processor for storing prede-

45 fined parameter data values. An autocalibration code is
associated with the sensor and read by the processor
before the user sample to be measured is received. The
autocalibration code is used in measuring the prede-
fined parameter data value to compensate for different

so characteristics of sensors which will vary on a batch to
batch basis.

Brief Description of the Drawings

55 The present invention together with the above and
other objects and advantages may best be understood
from the following detailed description of the preferred
embodiments of the invention illustrated in the draw-

2

3

ings, wherein:

FIG. 1 is an enlarged perspective view of a sensor
meter shown with the slide in an open position in
accordance with the present invention; 5

FIG. 2 is an enlarged perspective view of the sen-
sor meter of FIG. 1 with the slide in a closed posi-
tion;

10

FIG. 3 is an enlarged perspective view of the sen-
sor meter of FIG. 1 illustrating an interior thereof;

FIG. 4 is an enlarged perspective view of an exem-
plary sensor package illustrating a preferred is
arrangement of an autocalibration encoding label
attached to a diskette of sensors in accordance with
the present invention of the sensor meter of FIG. 1 ;

FIG. 5 is a block diagram representation of sensor 20
meter circuitry in accordance with the present
invention of the sensor of FIG. 1 ;

FIG. 6 A is a schematic diagram representation of
exemplary circuitry for use with a digital autocall 25
bration encoding label of the invention;

FIG. 6B is an expanded view of a digital autocali-
bration encoding label useful in the present inven-
tion; 30

FIG. 6C is a chart illustrating an alternative digital
autocalibration encoding label in accordance with
the present invention of the sensor meter of FIG. 1

35

FIG. 6D is a chart illustrating further alternative dig-
ital autocalibration encoding labels in accordance
with the present invention of the sensor meter of
FIG. 1

40

FIG. 7A is a schematic diagram representation of
exemplary circuitry for use with an analog autocali-
bration encoding label of the invention;

FIG. 7B expanded views of alternative analog auto- 45
calibration encoding labels useful in the present
invention;

FIG. 7C expanded views of alternative analog auto-
calibration encoding labels useful in the present so
invention;

FIG. 7D is a chart illustrating further alternative
analog autocalibration encoding labels in accord-
ance with the present invention of the sensor meter 55
of FIG. 1;

FIGS. 8, 9. 10, and 11 are flow charts illustrating

4

logical steps performed in accordance with the
present invention of the autocalibration encoding
method by the sensor meter of FIG. 1.

Detailed Description of the Preferred Embodiments

Making reference now to the drawings, in FIGS. 1,
2 and 3 there is illustrated a sensor meter designated as
a whole by the reference character 10 and arranged in
accordance with principles of the present invention.
Sensor meter 10 includes a clam-shell type housing
enclosure 12 formed by a base member 14 and a cover
member 16. Base and cover members 14 and 16 are
pivotably attached together at a first end 18 and are
secured together by a latch member 20 at a second,
opposite end 22. A display 24, such as a liquid crystal
display (LCD) is carried by the cover member 16. To
turn the sensor meter 10 on and off, a manually mova-
ble slide 28 mounted on the cover member 16 is moved
between an open position shown in FIG. 1 and a closed
position shown in FIG. 2.

In the closed or OFF position of FIG. 2, the slide 28
covers the display 24. A thumb grip 30 carried by the
slide 28 is arranged for manual engagement by a user
of the sensor meter 10 to select the ON and OFF posi-
tions. The thumb grip 30 also is movable from left to
right in the OFF position of slide 28 for selecting a sys-
tem test operational mode. When a user moves the
slide 28 to the ON position of FIG. 1 , the display is
uncovered and a sensor 32 is presented. The sensor 32
extends through a slot 34 and is positioned outside the
enclosure 12 for the user to apply a blood drop. A right
button 42 and a left button or switch 44 (or switches A
and B in FIG. 7) are carried by the enclosure 12 for
operation by a user to select predefined operational
modes for the sensor meter 10, and for example, to set,
recall and delete blood glucose readings and to set
date, time, and options.

Referring now to FIGS. 3 and 4, in FIG. 3, the inside
of the sensor meter 10 is shown without a sensor pack-
age. An exemplary sensor package generally desig-
nated by the reference character 50 is separately
illustrated in FIG. 4. Sensor meter base member 14
supports an autocalibration plate 52 and a predeter-
mined number of autocalibration pins 54, for example,
ten autocalibration pins 54, as shown. The autocalibra-
tion pins 54 are connected via a flex circuit 56 and an
autocalibration connector 58 to associated sensor cir-
cuitry 81 as illustrated and described with respect to
FIG. 5, and FIG. 6A or FIG. 7A. Sensor circuitry 81 is
located in the upper part of the sensor meter 10
between the cover 16 and a block guide 60. A disk
retainer 66 and an indexing disk 64 are provided within
the cover member 16. The indexing disk 64 includes a
pair of locking projections 65 for engagement with coop-
erative triangular shaped recessed portions 35 of the
sensor package 50 for receiving and retaining the sen-
sor package 50 on the indexing disk 64. Sensor pack-

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age 50 carries an autocalibration label generally
designated by the reference character 70 (170 in FIG.
7B or 170A in FIG. 7C).

In accordance with the invention, calibration codes
assigned for use in the clinical value computations to s
compensate for manufacturing variations between sen-
sor lots are encoded upon a tag or label generally des-
ignated by 70 that is associated with a sensor package
50 of sensors 32, as shown in Fig 4. The calibration
encoded label 70 is inserted into the instrument with the w
package 50 of multiple sensors 32 which are stored in
individual blisters 33 and read by associated sensor
electronic circuitry before a sensor 32 is used. Calcula-
tion of the correct test values, such as, glucose values
from current readings, is based upon solving a single is
equation. Equation constants based on a calibration
code are identified, such as by either using an algorithm
to calculate the equation constants or retrieving the
equation constants from a lookup table for a particular
predefined calibration code read from the calibration 20
encoded label 70. The calibration encoded label 70 can
be implemented by digital, mechanical, analog, optical
or a combination of these techniques.

Referring to FIG. 4, the sensor package 50 used in
a sensor meter 1 0 for handling of a plurality of fluid sen- 25
sors 32. The sensor package 50 includes a plurality of
sensor cavities or blisters 33 extending toward a periph-
eral edge of the sensor package 50. Each sensor cavity
33 accommodates one of the plurality of fluid sensors
32. The sensor package 50 is generally circular in 30
shape with the sensor cavities 33 extending from near
the outer peripheral edge toward and spaced apart from
the center of the sensor package 50. The sensor pack-
age 50 includes an autocalibration data area generally
designated by 70 providing autocalibration encoded 35
information. This autocalibration encoded information or
autocalibration label 70 includes a plurality of contact
pads 72 aligned for electrical contact engagement with
the autocalibration pins 54 when the sensor package 50
is received within the sensor meter 1 0. The autocalibra- 40
tion label 70 includes an inner conductive path or trace
74 and an outer conductive path 76. As described in
detail below, selected contact pads 72 are connected to
the conductive paths 74 and 76.

Referring also to FIG. 5, there is shown a block dia- 45
gram representation of sensor circuitry designated as a
whole by the reference character 81 and arranged in
accordance with principles of the present invention.
Sensor circuitry 81 includes a microprocessor 82
together with an associated memory 84 for storing pro- so
gram and user data. A meter function 86 coupled to
sensor 32 is operatively controlled by the microproces-
sor 82 for recording blood glucose test values. A battery
monitor function 88 is coupled to the microprocessor 82
for detecting a low battery (not shown) condition. An 55
alarm function 89 is coupled to the microprocessor 82
for detecting predefined system conditions and for gen-
erating alarm indications for the user of sensor meter

10. A data port or communications interface 90 couples
data to and from a connected computer (not shown). An
ON/OFF input at a line 28A responsive to the user
ON/OFF operation of the slide 28 is coupled to the
microprocessor 82 for performing the blood test
sequence mode of sensor meter 10. A system features
input at a line 30A responsive to the user operation of
the thumb grip 30 is coupled to the microprocessor 82
for selectively performing the system features mode of
sensor meter 10. An autocalibration signal input indi-
cated at a line 70A is coupled to the microprocessor 82
for detecting the autocalibration encoded information for
the sensor lot in accordance with the invention. Micro-
processor 82 contains suitable programming to perform
the methods of the invention as illustrated in FIGS. 8, 9,
10and11.

FIG. 6A illustrates a digital electronic circuit 100 for
a digital calibration method which connects the proces-
sor 82 to the label 70. Ten digital output signals from the
processor 82 (OA through OJ) connect through ten driv-
ers 102 (DA through DJ) to the ten autocalibration pins
54 (PA through PJ) via the corresponding one of ten p-
channel field-effect transistors (FETs) 104 (TA through
TJ). The ten autocalibration pins 54 connect to ten
receivers 106 (RA through RJ) that provide ten digital
input signals (IA through U) to the processor 82. Each
receiver has an associated pull-up 108 (PU) connected
to a supply voltage VCC. The autocalibration pins 54
(PA through PJ) electrically connect to other label con-
tacts 72 on the autocalibration label 70 when the cover
16 is closed and a label 70 is present due to the conduc-
tive patterns printed on the particular label 70, for exam-
ple as shown on labels 70 in FIGS. 4 and 6B.

In operation to read a contact pattern of the label
70, the processor 82 turns on one of the drivers 102, all
other drivers 102 are turned off. The enabled driver 102
presents a low signal to the associated autocalibration
pin 54. The corresponding receiver 106 for the enabled
driver 102 directly connected to the associated autocal-
ibration pin 54 reads as a low signal since this particular
driver 102 and receiver 106 are directly connected. All
other receivers 106 whose autocalibration pin 54 is also
driven low due to the low resistance connection pro-
vided by the conductive traces 74, 76, 78 on the label 70
also read as a low signal. All remaining other receivers
102 read as a high signal since the associated driver
104 is not turned-on and the associated pull-up 108
pulls the receiver voltage to VCC.

Referring to FIG. 6B, there is shown an enlarged
view illustrating a preferred arrangement of the calibra-
tion encoded label 70 of the invention. In accordance
with a feature of the invention, the calibration encoded
label 70 is used to automate the process of information
transfer about the lot specific reagent calibration assign-
ment for associated sensors 32. For example, the auto-
calibration information as illustrated in FIG. 6B can be
encoded into the label 70 that is appended to the bottom
side of a blister-type package 50 that contains, for

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example, ten sensors 32 (one in each of 10 Individual
blisters 33) of a common origin or lot. The calibration
encoded label 70 is read at any angular position and
deciphered by the sensor meter 10 without any user
intervention. The calibration encoded label 70 is read
via the plurality of contacts 72 provided at predeter-
mined positions. As shown also in FIG. 4, selected ones
of the contacts 72 are connected to an inner ring or path
74, other contacts 72 connected to an outer ring or path
76, and other contacts 72 not connected.

A number of both digital and analog arrangements
can be employed to define the calibration encoded label
70 of FIGS. 4 and 6B ( the calibration encoded label 170
of FIG. 7B, and the calibration encoded label 170A of
FIG. 7C. The calibration encoded label 70, 170, and
170A can be constructed by screenprinting conductive
ink onto a base substrate, that can either be a separate
substrate or the outer sensor package surface 50, as
illustrated in FIGS. 4 and 6B. A separate substrate can
be attached to the sensor package 50 using an adhe-
sive, either a hot melt, UV-cure or fast-curing adhesive.
A conductive ink defining calibration encoded label 70,
170, and 170A preferably is a carbon, silver or a car-
bon/silver blended ink. The substrate 50 is any print
receptive surface including paper, polymer-filled paper
or polymer substrate, preferably a heat stabilized poly-
ethyleneteraphthalate (PET) or polycarbonate. Digital
calibration encoding can be defined by either direct
encoding through printing or cutting traces with a laser,
such as a C0 2 or Nd:YAG laser, for a particular sensor
lot. An analog system as illustrated and described with
respect to FIGS. 7A, 7B, 7C and 7D can be used that is
based on measuring resistors that are selectively
located at predefined positions, for example, repre-
sented by lines 152 and connected to the selected con-
tacts O, I, J as shown in FIG. 7B. In the analog label 1 70
or 170A, resistors at lines 152, or R1 and R2, preferably
are of the thick film type applied to the label by standard
screen printing technology.

Another feature as shown in FIGS. 4 and 6B of the
calibration encoded label 70 is an indicator feature rep-
resented by an arrow labeled 80 that replaces one or
more non-connected contact 72. Indicator arrow 80
advantageously is used for maintaining a remaining
sensor count number displayed to the user of sensor
meter 10. Indicator arrow 80 defines a starting or home
position of the sensor package 50, so that in those
instances when the package of sensors 32 is removed
from the instrument 10 and then is re-installed for what-
ever reason, an accurate remaining sensor count
number is enabled. To maintain the remaining sensor
count, the sensor package 50 is positioned so that the
arrow 80 on the autocalibration label 70 aligns to a pre-
determined instrument position when the sensor pack-
age 50 is inserted in sensor meter 10. The user
advances the sensor package 50 (repeatedly if neces-
sary) until a sensor 32 is made available. At this point a
sensor counter reflects the proper number of remaining

tests.

FIG. 6B illustrates an exemplary trace pattern for
calibration encoded label 70. As shown in FIG. 6B,
autocalibration label 70 includes three sets of contact

5 connections, first contacts 72, TO, A, D and E con-
nected to the outer ring or path 76 representing a logical
1 , second contacts 72, Tl, B. C, F connected to the inner
ring or path 74 representing a logical 0; and third null
contacts or no connection representing the home posi-

io tion or sync. It should be understood that the inner and
outer rings 74 and 76 do not have to be complete rings
or circles. The label contacts 72 and the traces that form
the inner and outer rings 74, 76 are made of an electri-
cally conductive material. The position of the contacts

15 72 are aligned with autocalibration pins 54 (shown in
FIG. 3) in the sensor meter 10 to make electrical con-
tact Although the calibration encoded label 70 can be
positioned in any one of multiple, for example, ten rotary
positions as the sensor package 50 is rotated, the label

20 contacts 72 will always be in alignment with pins 54 in
the sensor meter 10 when the calibration encoded label
70 is read.

The text which identifies the contacts does not actu-
ally appear on the calibration encoded label 70. The

25 arrow 80 is a visual aid to help the user orientate the
package 50 containing the label 70 in the instrument.
The arrow 80 need not be electrically conductive. The
two sync contacts 72 are not actually present on the
label, since they are not connected to any other of the

30 multiple contacts 72. A variation of label 70 could
include electrically connecting the sync contacts 72
together. The positions of the sync contacts 72 would be
on either side of the arrow 80 in FIG. 6B. The contact
labeled Tl (Tied Inner) always connects to the inner ring

35 74, and the contact labeled TO (Tied Outer) always con-
nects to the outer ring 76. The contacts labeled A
through F connect to both rings in an unprogrammed
label. A cut is made in the printed conductive label
material to disconnect the contact from the inner or

40 outer ring 74 or 76 in order to program the calibration
code into the label 70. Each one of the contacts A
through F could be connected to either ring, this repre-
sents 2 6 = 64 possible combinations. Code 0 (A through
F all connected to inner ring) and code 63 (A through F

45 all connected to outer ring) are not permitted, so 62
codes can be programmed with calibration encoded
label 70. In order to determine which contacts 72 are
the sync contacts, and which contacts 72 are connected
to the inner and outer rings 74 and 76, one contact 72 at

so a time is set as a low output (Zero). Any contacts 72 that
are on the same ring 74 or 76 as the low contact will
also register low due to the electrical connection pro-
vided by the conductive traces on the label 70. Because
the sync contacts are not connected to either ring 74 or

55 76. they register as the only low contact when either is
set low. This means that there must be at least two con-
tacts connected to each ring, otherwise, it would be
impossible to determine which contacts are the sync

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contacts.

A method for determining the autocalibration
number can use four readings of the autocalibration
label 70. Each of the readings is for one set of the con-
tacts 72; the set connected to the inner ring 74, the set s
connected to the outer ring 76, one sync contact, or the
other sync contact. After only four readings are taken, it
is possible to determine which contact 72 corresponds
to which of the four sets. The position of the sync con-
tacts are determined and this is used in conjunction with w
the reading from the set connected to the inner ring 74
to determine the autocalibration number. The contacts
72 connected to the inner ring 74 are considered logical
zeroes, and the contacts 72 connected to the outer ring
74 are considered logical ones. is

A selected predefined calibration encoded pattern
consists of the conductive pads 72 interconnected by
the conductive inner and outer rings 74 and 76. Calibra-
tion data is encoded using selectively electrically inter-
connected sets of contacts on the label 70. One or more 20
null contact positions (between contacts A and Tl at
arrow 80 in FIG. 6B) are isolated from both rings 74 and
76 to serve as a rotary position index. One of the con-
tacts 72 at some known position relative to the sync
position 80 represented by contact TO connects to the 25
outer ring 76 so all connections to this contact TO are
logical ones. To detect a connection to the inner ring 74
or outer ring 76, at least two connections to that ring are
needed to detect continuity. The remaining pads 72 are
connected to one or the other rings 74 and 76, the par- 30
ticular connection pattern identifying the calibration
code. To minimize label stock, a single pattern advanta-
geously is used with subsequent punching or cutting to
isolate selectively each of six pads, positions A through
F, from one of the two rings 74 or 76. All contacts 72, 35
positions A through F, Tl and TO, except the index or
null positions, are connected to one, and only one, of
the two rings 74 or 76. A minimum of two pads 72 are
connected to each ring 74 and 76. This arrangement
facilitates error checking since all of the pads 72 except 40
for the index or sync contact 72 must be accounted for
in one of two continuity groups for a reading to be con-
sidered valid. A missing label 70 is detected when all
contacts appear to be a sync contact; i.e., there are no
electrical connections between meter pins 54 because 45
the continuity provided by the label 70 is missing.

In one digital encoding method a series of open and
closed circuits representing 0 and 1 are introduced onto
a label 70. An autocalibration digital label 70 is encoded
by laser cutting or printing to represent a particular cali- so
bration code number determined by the connections to
the inner ring 74, for example, where A represents 1 , B
represents 2, C represents 4, D represent 8, D repre-
sents 16 and F represents 32. In FIG. 6B, contacts B, C.
and F are connected to the inner ring 74 to define the 55
calibration code number.

Under software control illustrated and described
with respect to FIG. 1 1 , microprocessor 82 configures

one contact 72 or bit as a low while the other remaining
contacts high. All contacts 72 electrically connected to
the particular driven contact 72 are forced low while the
remaining contacts are pulled high. By selectively driv-
ing contacts 72 and reading the resulting input patterns,
the interconnection pattern and associated calibration
code is determined. While the unique home or sync
position defined by no connection to another contact is
used to identify how many sensors 32 remain in the
package 50 and to determine the rotary position of the
calibration encoded label 70 so that the label contacts
72, A through E, TO and Tl can be identified, it should
be understood that other configurations can be used
with unique patterns of bits to both encode starting posi-
tion and the calibration code. However, other binary
coding schemes provide fewer possible codes for the
calibration code number with the same number of label
contacts 72.

Alternative calibration encoded labels 70A and 70B
for encoding of the calibration information are illustrated
in FIGS. 6C and 6D, respectively. In any label 70, 70A
and 708, the actual physical locations of the contacts
relative to each other is not important for decoding the
label 70 as long as they are in known or predefined
positions.

Referring to FIGS. 6C and 6D, ten label contacts 72
are represented by contact A through contact J. As in
FIG. 68, there are three groupings or sets of contact
connections including null or SYNC, outer ring 76 or
OUTER, and inner ring 74 or INNER. In FIG. 6C for the
calibration encoded label 70A with ten contacts A
through J, one contact must be the SYNC shown as
contact A and one must be tied to the outer ring shown
as contact B, and the remaining eight contacts C
through J are connected to either the inner ring 74 or
the outer ring 76. The eight contacts C through J (codes
0 through 255) represent 256 (2 8 ) possible combina-
tions of connections, minus eight combinations for only
one inner ring connection (codes 127, 191, 223, 239,
247, 251, 253, 254), minus one combination for only
one outer ring connection (code 0). Calibration encoded
label 70A provides 247 unique combinations or codes
for the calibration number.

The calibration codes on a particular label 70 can
also be used to distinguish between several types of
sensors 32. Suppose sensor type "A" required 10 cali-
bration codes, sensor type "B" required 20 calibration
codes, and sensor type "C" required 30 calibration
codes. The autocaJibration codes could be assigned so
codes 1 through 10 signify a type "A" sensor with type
"A" calibration code 1 through 10, label codes 11
through 30" signify a type "B" sensor with type "B" cali-
bration code 1 through 20, and label codes 31 through
60 signify a type "C" sensor with type "C" calibration
code 1 through 30. In this way the label code indicates
both the sensor type and calibration code associated
with that sensor type.

In FIG. 6D, alternative types 1 , 2, 3 and 4 of the cal-

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ibration encoded labels 706 include two sync positions.
In the type 1 calibration encoded label 70B two adjacent
sync positions are used which advantageously corre-
sponds to an arrow indicator 80 as shown in FIGS. 4
and 6B to help the user with positioning the label in the
sensor meter 10. With the type 1 label 70B, the two
adjacent sync contacts are A and B, one contact J is
tied to the outer ring 76, and the seven remaining con-
tacts C through I are connected to the inner or outer ring
74 or 76. The seven contacts represent 128 (2 7 ) possi-
ble combinations of connections, minus seven combina-
tions for only one inner ring connection, minus one
combination for only one outer ring connection. The
type 1 calibration encoded label 70B provides 120
unique combinations for the calibration number.

With the type 2, 3 and 4 calibration encoded labels
70B, the relative position of the two sync contacts can
be used to provide additional information. Sync contact
combinations A and B (no gap) type 1 , A and C (gap of
1 space) type 2, A and D (gap of 2 spaces) type 3, and
A and E (gap of three spaces) type 4 can be uniquely
detected and used to distinguish between four types of
calibration encoded labels 70B, each calibration
encoded label 70B encoding 120 unique combinations.
Sync contact combinations A and F, A and G, A and H,
A and I, and A and J are not uniquely distinguishable.
Using the four types 1, 2, 3, and 4 of calibration
encoded labels 70B provides a total of 480 (4*120)
combinations for the calibration number.

Other calibration encoded labels 70 can be pro-
vided with the relative position of three or more sync
contacts used to generate unique patterns. For exam-
ple, with three sync contacts and one contact tied to the
outer ring, six contacts remain to connect to the outer or
inner ring. The six contacts represent 64 (2 6 ) possible
combinations of connections, minus seven combina-
tions for only one inner ring connection, minus one com-
bination for only one outer ring connection which leaves
56 unique combinations There are many ways that the
three sync contacts can be uniquely placed: A, B, and
C; A, B, and D; A, B, and E; A, B, and F; A, B, and G; A,
B, and H; A, B, and I; A, C and E; A, C, and F; etc. As
with two sync contacts, these combinations of sync con-
tacts can indicate different types of labels, and for exam-
ple, to identify one of multiple types of analysis to be
performed by the sensor meter 10.

The preferred calibration encoded label arrange-
ment has two rings or paths 74 and 76 as illustrated in
FIG. 6B, with contacts connected to one ring, such as
ring 74 assigned as logical 0 the other ring 76 as logical
1 for a binary coding method. In another design varia-
tion, it is possible to have labels with additional conduc-
tors with connections to these conductors assigned as
logical 2 (ternary coding), logical 3 (quaternary coding),
and the lika This would permit more unique combina-
tions for a given number of label contacts 72.

in FIG. 7A, an analog system generally designated
by reference character 150 is shown. Analog system

150 is based on measuring resistance values of resis-
tors 152 (R1 and R2) provided on a label 170, or label
170A of FIG. 7C. The resistance value of resistors 152
(R1 and R2) provides the calibration value. Although it is

5 possible to relate the analog value of the resistance to
the calibration value, the preferred arrangement is to
print resistors 152 of specific values. For example, to
distinguish five calibration codes one of five different
resistance values (e.g. 1000O, 2000U 3000O, 4000P,

10 5000O) would be screen printed onto the label 1 70 or
170A. The resistance values for resistors 152 (R1 and
R2) are chosen so the resistance values measured by
the processor 82 are easily distinguished from each
other even though there may be variations in the resist-

75 ance due to printing variations or variations in contact
resistance where the label 170 or 170A is contacted by
the autocalibration pins 54.

In FIG. 7A, VREF is a known reference voltage and
resistor 154 RREF is a known reference resistance. An

20 analog-to-digital converter (ADC) 1 56 converts the ana-
log voltage present at its input labeled VMEAS into a
digital value at its output labeled (IA) which is read by
the processor 82. A driver 1 58 (DA) is an analog switch
controlled by the processor 82 through a signal line

25 labeled OA. The driver 158 controls a p-channel field-
effect transistor (FET) 160 that leaves resistor 154
RREF in the circuit 150 when the driver 158 is turned off
or shorts out resistor 154 RREF when the driver 158 is
turned on.

30 The value of resistors 152 (R1 and R2) can be
determined as follows. With driver 158 DA turned off,
resistor 154 RREF is in the circuit, so resistors 152 (R1
and R2) plus resistor 154 RREF function as a voltage
divider. Then the voltage VMEAS is measured and

35 defined as VOFF. With driver 158 DA turned on, RREF
is shorted out, so resistors 152 (R1 and R2) function as
a voltage divider. Then the voltage VMEAS is again
measured and now defined as VON.
The applicable equations are:

40

VOFF = ^J^^-.- VREF

R1+R2+RREF

45

50

VON:

solving eqn2for R1:

R1 = R2

R2

R1 + R2

VREF

VREF -VON
VON

[eqnl]

[eqn2]

[eqn3]

substituting R1 into eqn 1 and solving for R2:

n?-RREF VQN (V^F -VOFF)

R2 - RREF VREp j^gpp : VQN) [eqn 4]

7

13

EP0 840 122 A2

14

VREF and RREF are known values and VOFF and VON
are measured values. In eqn 3 the values for R2, VREF,
and VON are substituted to calculate R1. At this point
R1 and R2 are known so the calibration value can be
determined. 5

To distinguish many calibration codes, more than
one resistor could be used. For a label 70 with m resis-
tors where each resistor may be any of n values, then
the number of calibration codes is m n .

For example, printing two resistors 152 (R1 and R2) 10
where each resistor 150 could have one of five distinct
resistance values permits 25 (i.e. 5*5 or 5 2 ) calibration
codes to be distinguished. This can be expanded to
three resistors 152 could provide 125 (i.e. 5*5*5 or 5 3 )
calibration codes, and so on. is

Having reference to FIG. 7B, an analog two resistor
label 1 70 is illustrated. An inner resistance 1 52 (R2) and
outer resistance 152 (R1) can be replicated ten times
(once for each rotary position of the sensor package 50)
while only three autocalibration pins 54 are needed, as 20
shown in FIG. 7A. The autocalibration pins 54 are
placed in a line. One pin 54 (PA) would contact the con-
tact pad at the common junction (I) of ail the inner resis-
tors 152 (R2). Another pin 54 (PB) contacts a junction
(J) of the inner resistor R2 and the outer resistor 152 25
R1 . The third pin 54 (PC) contacts the other end (O) of
the outer resistor 152 (R1).

A variation of the label 1 70 of FIG. 7B can have only
one inner resistor 152 (R2) and one outer resistor 152
(R1), with continuous conductive rings to make contact 30
with the autocalibration pins 54. One ring (not shown)
would be at the diameter of the junction (J) of resistors
152 (R1 and R2). The other ring (not shown) would be
located at the diameter of the other end (O) of resistor
152 R1. The conductive rings would be made of low 35
resistance material. The meter autocalibration pins 54
would contact the center contact (I) and the two rings,
as with the label 170.

Another style of two resistor label 1 70A is illustrated
in FIG. 7C. The three autocalibration pins 54 are placed 40
in a line. One pin 54 (PB) would contact the junction 1 76
of all ten resistors 152. Another pin (PA) would connect
to the end 174 of resistor R1. The third pin (PC) would
be in a line with the other two pins and connect to the
end 1 74 of resistor R2. If the set of resistance values for 45
resistance R1 (e.g. n1 values) were different than the
set of resistance values for resistance R2 (e.g. n2 val-
ues) then m *n2 different calibration codes could be dis-
tinguished.

For the FIG. 7C style label 170A, where values of so
the two resistors 152 are chosen from the same set of n
resistances then some combinations are not distin-
guishable because the label rotates, e.g. R1 = 1000O
and R2 = 2000O can not be distinguished from R1 »
2000Q and R2 = 1 0OOfl The number of different combi- 55
nations of two resistors of the style of Figure B where
each resistor may be one of n values is given by the
equation:

tfn-1) „

Having reference to FIG. 7D, the number of different
resistance values and the number of distinct calibration
codes than can be determined is tabulated.

Referring to FIG. 8. sequential steps performed by
microprocessor 82 begin at a block 800 with initializing
the hardware and software of sensor meter 10. An ON
input at line 28A (FIG 5) is identified as indicated at a
decision block 802. Microprocessor 82 processes a day
rollover as indicated at a block 804. When the ON input
is identified at block 802, checking for both A(44) and
B(42) buttons pressed is provided as indicated at a
decision block 806. When both A(44) and B(42) have
been pressed, a manufacturing mode is processed as
indicated at a block 810. Otherwise, a system check is
performed as indicated at a block 812. Then checking
for B(42) pressed is provided as indicated at a decision
block 814. If B(42) has been pressed, then a customer
service mode is processed as indicated at a block 816.
Otherwise, the mode switch is checked as indicated at a
decision block 818. When the test selection is identified
at block 818, then the test mode is processed as indi-
cated at a block 820. When the feature selection is iden-
tified at block 818, then the feature mode is processed
as indicated at a block 822. Microprocessor 82 proc-
esses sensor shutdown as indicated at a block 823 and
poweroff as indicated at a block 824.

Referring to FIG. 9, sequential steps performed by
microprocessor 82 for system checking begin with
checking for an open switch status as indicated at a
block 900. Microprocessor 82 checks the integrity of
memory 54 as indicated at a block 902. Microprocessor
82 checks the calibration encoded label 70 in accord-
ance with the invention as indicated at a block 904.
Exemplary steps performed for reading and decoding
the calibration encoded label 70 are further illustrated
and described with respect to FIG. 10. Microprocessor
82 checks a battery changed bit to identify a low or dead
battery as indicated at a block 906. Microprocessor 82
enables 1 second, 1/4 second, and key press interrupt
as indicated at a block 91 0.

Referring to FIG. 10. sequential steps performed by
microprocessor 82 for the test mode begin with waiting
for an applied blood sample as indicated at a block
1000. When the user applies a blood sample to the sen-
sor 32 that is identified at block 1000. then the micro-
processor 82 starts a 30 second countdown as
indicated at a block 1002. A glucose value is calculated
by the microprocessor 82 using the calibration code
value read at block 904 in FIG. 9, as indicated at a block
1004. The glucose value is displayed for viewing by the
user as indicated at a block 1008. Microprocessor 82
processes shutdown as indicated at a block 1010.

Referring to FIG. 1 1 , sequential steps performed by
microprocessor 82 for decoding the calibration encoded

10

15

8

15

EP 0 840 122 A2

16

label 70 are shown. The sequential operations begin
with microprocessor 82 setting the least significant bit
(LSB) low, the remaining bits high, and taking a reading
as indicated at a block 1 100. Microprocessor 82 deter-
mines from the first reading the Position of the first bit in
the label 70 that is not connected to the least significant
bit, and this bit is set low, the remaining bits high, and a
second reading is taken as indicated at a block 1102.
This bit set low before the second reading is the first, or
least significant bit that is a 1. Microprocessor 82 deter-
mines the first bit that was connected to neither of the
above sets which is the least significant bit that is a 1 in
both readings, sets this bit low, the remaining bits high,
and takes the third reading as indicated at a block 1 104.
Microprocessor 82 determines the first bit that was con-
nected to none of the above sets which is the least sig-
nificant bit that is a 1 in previous three readings, sets the
identified bit low, the remaining bits high, and takes the
fourth reading as indicated at a block 1106. Microproc-
essor 82 determines which of the four readings isolates
the sync contacts where the readings have only one
zero bit as indicated at a block 1 1 08. Microprocessor 82
determines which of the remaining two readings is from
the outer ring 76 and which one is from the inner ring 74
as indicated at a block 1110. Identifying the inner and
outer rings 74 and 76 is done using the position of the
sync bits identified at block 1 108, and the known fixed
pattern of the Tl and TO contacts. Microprocessor 82
uses the position of the sync bits and the reading of the
inner ring to determine the autocalibration number as
indicated at a block 812. For example, the bits defining
the autocalibration number can include bits FEDCBA.

In the four readings, no bit can be present, or con-
nected, for more than one reading. In other words, a bit
can be a zero in only one of the four sets. The zeroes in
all four sets are mutually exclusive. Two of the four read-
ings must be for the sync positions. That is, two of the
readings must have only one zero and these must be in
adjacent positions. The pattern of the TO and Tl bits
must exist exactly. That is, all connections to contact TO
are assigned logical 1 , connections to contact Tl are
assigned logical 0 and contacts TO and Tl can not be
connected together. Microprocessor 82 looks for this
exact circumstance, based on the position of the sync
contacts. The autocalibration number identified at block
812 must be between 1 and 62, inclusive.

A digitally implemented calibration encoded label
70, 70A or 70B has several advantages. First with the
sensor package 50 rotated within the sensor meter 10
to any or multiple rotary positions with the digitally
encoded calibration encoded label 70, 70A or 70B
including at least one allocated position to define a
home, i.e., the contact pad position without any connec-
tions to either ring 74 or ring 76, the software for deci-
phering the calibration code is simplified. Second, the
inner and outer rings 74 and 76 with connecting traces
provide a means of determining if the instrument has
made contact to the calibration encoded label properly.

The digitally encoded autocalibration label 70, 70A or
70B can be encoded by cutting either trace at those
position that have both traces. Sensing of those posi-
tions connected along the inner ring 74 provides calibra-

5 tion information, while sensing of the remaining
positions verifies that the contact pins have made con-
tact to those positions properly. It is believed that most
common failure mode will be improper contact to the
label or an open circuit An error is also detectable when

10 neither trace is cut. Third, a digital system is more
robust with respect to signal detection. In an analog or
resistive version, careful control of the print thickness,
the inks and the contact resistance are necessary to dif-
ferentiate different calibration levels. While these

15 parameters are still important for a digital system, the
requirements can be relaxed without compromising the
information contained in the label. Fourth, the process
for producing the digital calibration encoded label 70 is
simplified to a single printing step and subsequent

20 marking. An analog version of calibration encoded label
70 requires multiple print steps with different inks to pro-
duce a complete label. Fifth, the number of possible cal-
ibration lines can approach 256 or 2 8 . This number of
calibration lines provides excess capacity and flexibility

25 that could not be obtained easily with an analog system.
Also, extra positions, such as, Tl and T2, in FIG. 6 A can
be used to increase the number of calibration lines
beyond 64 or could be used to designate different prod-
ucts, such as, a test sensor 32 for testing a particular

30 parameter other than glucose. Finally, the use of a sin-
gle label which is marked to encode information
reduced processing costs and inventory requirements.
Processing costs are reduced because a single ink is
required for label printing. Several conductive inks, each

35 with a different resistivity, are required in the analog
scheme. Inventory costs are minimized because the
same label is produced each time. When the calibration
level has been determined, the digital calibration
encoded labels 70 are marked by cutting the appropri-

40 ate traces. It should be understood that the digital cali-
bration encoded labels 70 can be encoded by printing
labels without the appropriate traces to the inner ring 74
or outer ring 76.

While the present invention has been described

45 with reference to the details of the embodiments of the
invention shown in the drawings, these details are not
intended to limit the scope of the invention as claimed in
the appended claims.

so Claims

1 . A system for determination of anaJyte concentration
in a test sample comprising:

55 sensor means for receiving a user sample;

processor means responsive to said sensor
means for performing a predefined test
sequence for measuring a predefined parame-

9

17

EP0840122 A2

18

ter value; and

autocalibration code means, operatively asso-
ciated with the sensor means, coupled to said
processor means for providing autocalibration
encoded information read by the processor, 5
said autocalibration encoded information being
utilized by the processor for said predefined
test sequence.

2. A system as recited in claim 1 wherein said autocal- io
ibration code means comprise a plurality of electri-
cal contacts defining a predefined encoded bit
pattern defining a sync position and a calibration
code.

15

3. A system as recited in claim 2 wherein said plurality
of electrical contacts defining said autocalibration
encoded information include at least two sync con-
tacts defining said sync position, said at least two
sync contacts being positioned relative to each 20
other for encoding predefined information.

4. A system as recited in claim 3 wherein said at least
two sync contacts including a predefined one of
multiple relative position combinations between 25
sync contacts of no gap, a gap of one space, a gap

of two spaces, and a gap of three spaces.

5. A system as recited in claim 1 wherein said autocal-
ibration encoded information is defined by electri- 30
cally interconnected sets of contacts on a label
carried by said sensor means.

6. A system as recited in claim 1 further includes an
enclosure, said enclosure formed by a base mem- 35
ber and a cover member; said cover member and
said sensor means include cooperating means for
receiving and positioning said sensor means; and
said base means supports a predetermined
number of autocalibration pins. 40

7. A system as recited in claim 6 wherein said base
member and said cover member are pivotably
attached together at a first end and are secured
together by a latch member at a second, opposite 45
end; and said autocalibration code means com-
prises a label defining said autocalibration encoded
information and wherein said label is carried by a
package containing multiple sensor means.

50

8. A method for calibrating a sensor system compris-
ing the steps of:

providing the sensor system with a sensor for
receiving a user sample and a processor for 55
performing a predefined test sequence for
measuring a predefined parameter value;
providing calibration encoded information with

said sensor, and

reading said calibration encoded information
by said processor and utilizing said calibration
encoded information for said predefined test
sequence.

9. A method for calibrating a sensor system as recited
in claim 8 wherein said step of providing calibration
encoded information with said sensor includes the
step of defining a calibration encoded label on a
package containing said sensor.

10. A method for calibrating a sensor as recited in claim
8 wherein said step of providing calibration
encoded information with said sensor includes the
step of applying an electrically conductive calibra-
tion encoded pattern on a substrate operatively
associated with said sensor.

10

EP 0 840 122 A2

FIG. 2

11

EP 0 840 122 A2

FIG. 3

33

FIG.4

32.

70

35 3 , 2 3 3 74 3 , 5 32

33
72

35

32-
33.

33

35'

50
32

•33
32

32'

35

32

35 76 32 33

33

32

12

EP0 840 122 A2

28A"

30A-

70A

MEMORY
84

ON/OFF
INPUT

SYSTEM
FEATURE
INPUT

AUTOCALIBRATION
READING

MICROPROCESSOR
82

81

ALARM
89

DISPLAY
24

METER

SENSOR

86

< — )

32

BATTERY
MONITOR
88

FIG. 5

13

EP0 840 122 A2

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840122 A2

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EP 0 840 122 A2

INITIALIZE
HARDWARE AND
SOFTWARE
800

NO

POWER
ON SWITCH
602

YES

DAY
ROLLOVER
804

BOTHA
AND B PRESSED
806

YES

MANUFACTURING
MODE
810

FEATURE
MODE
822

FEATURE

FIG. 8

YFS

SHUTDOWN
823

r

(POWER A

CUSTOMER
SERVICE
MODE
816

19

EP0840122 A2

OPEN SWITCH
STATUS
CHECKED
900

CHECKSUMS
CHECKED
902

AUTOCAL
READ
904

BATTERY
CHANGED BIT
CHECKED
906

1 SEC, 1/4 SEC
AND KEY PRESS
INTERRUPT
ENABLED
910

FIG. 9

20

EP 0 840 122 A2

WAIT FOR
APPLIED
BLOOD
1000

30 SECOND
COUNTDOWN
1002

±

CALCULATE
GLUCOSE
1004

£

DISPLAY
GLUCOSE
1008

SHUTDOWN
1010

FIG. 10

EP 0 840 122 A2

FIG. 11

SET LSB LOW,
REMAINING BITS

HIGH, TAKE
READING 1100

DETERMINE POSITION

OF FIRST BIT NOT
CONNECTED TO LSB
AND SET THIS BIT LOW,
REMAINING BITS HIGH,
TAKE 2ND READING
1102

DETERMINE FIRST BIT
CONNECTED TO NEITHER
OF ABOVE SETS AND SET
THIS BIT LOW, REMAINING

BITS HIGH, TAKE 3RD
READING 1104

DETERMINE FIRST BIT
NOT CONNECTED TO
ABOVE SETS AND SET

THIS BIT LOW,
REMAINING BITS HIGH,
TAKE 4TH READING 1106

C RETURN J

IDENTIFY
CALIBRATION
NUMBER USING
POSITION OF SYNC
BITS AND INNER RING
READING 1112

IDENTIFY
OUTER RING
AND INNER RING
READINGS
1110

IDENTIFY
READINGS THAT
ISOLATE SYNC
BITS 1108

22